The present invention relates to a fuser apparatus for an electrophotographic reproducing machine and, more particularly, to an improved fuser apparatus for such machine having a fuser roll and pressure roll that forms a nip through which a recording medium with a toner image is passed to fuse the image thereto, and a cleaning web system for cleaning the fuser roll with means for preventing inadvertent spooling of the web from the supply roll during a recording medium jam clearance.
One type of electrophotographic reproducing machine is a xerographic copier or printer. In a typical xerographic copier or printer, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the xerographic process. As in most xerographic machines, a light image of an original document is projected or scanned onto a uniformly charged surface of a photoreceptor to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged powdered developing material called toner to form a toner image corresponding to the latent image on the photoreceptor surface. When the photoreceptor surface is reusable, the toner image is then electrostatically transferred to a recording medium, such as paper, and the surface of the photoreceptor is prepared to be used once again for the reproduction of a copy of an original. The paper with the powdered toner thereon in imagewise configuration is separated from the photoreceptor and moved through a fuser to permanently fix or fuse the toner image to the paper.
Typically, a fuser provides a combination of heat and pressure to form the permanent image on the paper. The basic architecture of a fuser is well known. Essentially, it comprises a pressure roll that rolls against a rotatable heated fuser roll to form a nip therebetween. A toner image-bearing sheet of paper is passed through the nip. The side of the paper having the toner image typically faces the fuser roll, which is often supplied with a heat source, such as a resistance heater, at the core thereof. The combination of heat from the fuser roll and pressure between the fuser roll and the pressure roll fuses the toner image to the paper, and once the fused toner cools, the image is permanently fixed to the paper.
In most fusing systems in use today, there is provided a system by which the fuser roll can be automatically cleaned and/or supplied with a lubricant or release agent. For high volume reproducing machines, the release agent is typically supplied from an open supply of liquid release agent that is ultimately applied to the fuser roll through one or more donor rollers. In contrast, for mid-volume to low volume reproducing machines, the cleaning and lubrication steps are provided to the surface of the fuser roll by means of a web. The web is urged against the surface of the fuser roll at a location generally away from the nip formed by the pressure and fuser rolls. The web provides a textured surface for removing particles of toner that remained on the fuser roll after the paper with the toner image has passed through the fuser. The web may also provide amounts of lubricant or release agent to the fuser roll. As is well known, the function of the release agent is to prevent sheets of paper that pass through the fuser nip from sticking to the surface of the fuser roll, thus causing a paper jam. In addition, the release agent minimizes the amount of toner that sticks to the fuser roll rather than remaining on the paper.
Generally, in most systems having a web for treating the fuser roll, the web is drawn from a replaceable supply roll and is moved at a reasonably slow rate relative to the movement of the fuser roll. Therefore, the motion of the fuser roll causes the surface of fuser roll to rub against a small area of the web. The relatively slow motion of the web provides friction to the fuser roll surface and provides a supply of clean web at a reasonable rate. A typical ratio of surface speeds, for example, in a 60 PPM printer, is approximately 300 mm per second for the outer surface of the fuser roll, while in contrast, the speed of the web is 2 to 3 mm per minute.
In most prior art designs of a web feeder for a fuser, the web is withdrawn from a supply roll and pulled by and wound on a take up roll. Typically, the take up roll is driven slowly and the supply roll idles passively. Many structures have been proposed for providing the necessary slow but continuous motion of the web. Some prior art techniques include supplying an external motor separate from the motor driving the fuser roll, or providing a solenoid or ratchet arrangement. It is also known to vary the speed of the take up roll as the circumference of the web on the take up roll increases. Otherwise, if the rotational speed of the take up roll remains constant, the increase in the web circumference will cause a significant increase in the web speed and exhaust the supply of web prematurely.
Paper jam clearance from fusers present serious problems to manufacturers of electrophotographic printers and copiers, especially when web cleaning systems are used. Usually, the cleaning web is undesirably pulled or spooled from the passively rotated supply roll when the jammed paper is removed while the pressure roll is still in pressure contact with the fuser roll. Inadvertent spooling of the cleaning web may require a skilled technician to rewind or replace the web. Many existing printers and copiers overcome this problem by providing complex and expensive devices which automatically separate the pressure roll from the fuser roll when a jam occurs. Though automatically separating the pressure roll from the fuser roll enables the jammed paper to be readily removed without causing inadvertent web spooling, this solution is too costly and better solutions are necessary to prevent web spooling.
U.S. Pat. No. 5,749,038 discloses a fuser subsystem for an electrophotographic printer or copier having a web which cleans the fuser roll. The web is driven by a mechanism that enables a constant velocity of the web relative to the fuser roll surface without the need of a separate motor or controller, as well as compensates for changes in frictional coefficient between the fuser roll and the web.
U.S. Pat. No. 5,049,944 discloses an apparatus in which a cleaning web is urged against a fuser roll, and a control system is used to vary the operation of the motor that moves the web, so that the web is driven at a relatively constant linear speed at the contact nip of the web with the fuser roll.
U.S. Pat. No. 5,200,785 discloses a fusing subsystem in a replaceable cartridge that includes a fuser roll, an oil applying structure, a heating lamp, temperature sensors, and an access opening. The cartridge electrical connector mates with a receiving electrical connector in reproducing machine.
U.S. Pat. No. 6,532,353 discloses a web cleaning mechanism for cleaning a fuser roll of a fuser assembly in a reproduction apparatus. The mechanism includes an elongated web of cleaning material supplied on a supply roll and a take up roll. A motor is coupled to the take up roll for selectively advancing the web against the fuser roll and onto the take up roll. An encoder associated with the motor produces a string of pulses while the motor is operative, and a logic and control unit activates the motor for a period of time in response to the number of pulses produced by the encoder.